U.S. patent application number 14/832909 was filed with the patent office on 2016-03-03 for multi-segment mach-zehnder modulator-driver system.
The applicant listed for this patent is Futurewei Technologies, Inc.. Invention is credited to Yu Sheng Bai.
Application Number | 20160062207 14/832909 |
Document ID | / |
Family ID | 55398759 |
Filed Date | 2016-03-03 |
United States Patent
Application |
20160062207 |
Kind Code |
A1 |
Bai; Yu Sheng |
March 3, 2016 |
Multi-Segment Mach-Zehnder Modulator-Driver System
Abstract
An optical modulator comprising a waveguide for propagating an
optical signal comprising a proximate arm configured to communicate
a proximate portion of the optical signal, and a distal arm
configured to communicate a distal portion of the optical signal, a
proximate diode configured to modulate the proximate portion of the
optical signal, a distal diode configured to modulate the distal
portion of the optical signal, and an electrical input electrically
coupled to opposite signed interfaces of the proximate diode and
the distal diode such that an electrical driving signal propagated
along the electrical input causes an equal and opposite modulation
of the proximate portion of the optical signal in the proximate arm
of the waveguide and the distal portion of the optical signal in
the distal arm of the waveguide.
Inventors: |
Bai; Yu Sheng; (Los Altos
Hills, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Futurewei Technologies, Inc. |
Plano |
TX |
US |
|
|
Family ID: |
55398759 |
Appl. No.: |
14/832909 |
Filed: |
August 21, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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62041544 |
Aug 25, 2014 |
|
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Current U.S.
Class: |
385/3 |
Current CPC
Class: |
G02F 1/2257 20130101;
G02F 1/225 20130101; G02F 2001/212 20130101 |
International
Class: |
G02F 1/225 20060101
G02F001/225 |
Claims
1. An optical modulator comprising: a waveguide for propagating an
optical signal comprising: a proximate arm configured to
communicate a proximate portion of the optical signal; and a distal
arm configured to communicate a distal portion of the optical
signal; a proximate diode configured to modulate the proximate
portion of the optical signal; a distal diode configured to
modulate the distal portion of the optical signal; and an
electrical input electrically coupled to opposite signed interfaces
of the proximate diode and the distal diode such that an electrical
driving signal propagated along the electrical input causes an
equal and opposite modulation of the proximate portion of the
optical signal in the proximate arm of the waveguide and the distal
portion of the optical signal in the distal arm of the
waveguide.
2. The optical modulator of claim 1, wherein the optical modulator
further comprises a plurality of proximate diode and distal diode
pairs positioned along the proximate arm of the waveguide and the
distal arm of the waveguide, and wherein each proximate diode and
distal diode pair modulates a portion of the electrical driving
signal onto the optical signal.
3. The optical modulator of claim 2, wherein each proximate diode
and distal diode pair is coupled to a single driver.
4. The optical modulator of claim 2, wherein each proximate diode
and distal diode pair is coupled to an electrical complement input
such that the electrical complement input is coupled to opposite
signed interfaces of each proximate diode and distal diode
pair.
5. The optical modulator of claim 4, wherein each proximate diode
and distal diode pair is coupled to a segment electrical input
between opposite signed interfaces of each proximate diode and
distal diode pair, and wherein the segment electrical input and the
electrical complement input comprise a common signal with opposite
electrical signs.
6. The optical modulator of claim 5, wherein the each segment
electrical input and corresponding electrical complement input are
received from a single driver.
7. The optical modulator of claim 1, wherein the electrical input
is electrically coupled to a cathode of the proximate diode and an
anode of the distal diode.
8. The optical modulator of claim 1, wherein the electrical input
is electrically coupled to an anode of the proximate diode and a
cathode of the distal diode.
9. The optical modulator of claim 1, wherein the optical modulator
comprises silicon, Indium Phosphide (InP), Gallium Arsenide (GaAs),
lithium niobate (LiNbO.sub.3), or combinations thereof.
10. A single-drive multi-segment optical modulator system
comprising: an optical modulator comprising: a plurality of
electrical segment inputs; a proximate waveguide arm configured to
communicate a proximate half of an optical signal; and a distal
waveguide arm configured to communicate a distal half of the
optical signal; and a plurality of modulator segments such that
each modulator segment is configured to modulate a corresponding
electrical segment input onto both the proximate waveguide arm and
the distal waveguide arm; and a drive circuit electrically coupled
to the optical modulator and comprising a plurality of drivers
corresponding to the plurality of modulator segments such that each
driver outputs an electrical segment signal to a single
corresponding electrical segment input to control modulation by a
single corresponding modulator segment.
11. The system of claim 10, wherein each modulator segment
comprises a proximate diode positioned across the proximate
waveguide arm and a distal diode positioned across the distal
waveguide arm.
12. The system of claim 11, wherein each electrical segment input
is coupled to a corresponding modulator segment such that the
electrical segment input is coupled to oppositely polarized
interfaces of the proximate diode and the distal diode.
13. The system of claim 12, wherein each electrical driver outputs
a complement electrical signal to a single corresponding electrical
segment, and wherein each complement electrical signal comprises an
equivalent amplitude and opposite charge to a corresponding
electrical segment signal.
14. The system of claim 13, wherein each complement electrical
signal is coupled to the corresponding modulator segment such that
the electrical segment input is coupled to oppositely polarized
interfaces of the corresponding proximate diode and the
corresponding distal diode.
15. The system of claim 14, wherein each complement electrical
signal is coupled to different oppositely polarized interfaces than
the corresponding electrical segment signal.
16. The system of claim 15, wherein each complement electrical
signal is coupled to an anode of a corresponding proximate diode
and a cathode of a corresponding distal diode, and wherein each
electrical segment signal is coupled to a cathode of the
corresponding proximate diode and an anode of the corresponding
distal diode.
17. The system of claim 15, wherein each complement electrical
signal is coupled to a cathode of a corresponding proximate diode
and an anode of a corresponding distal diode, and wherein each
electrical segment signal is coupled to an anode of the
corresponding proximate diode and a cathode of the corresponding
distal diode.
18. The system of claim 10, wherein the optical modulator comprises
silicon, Indium Phosphide (InP), Gallium Arsenide (GaAs), lithium
niobate (LiNbO.sub.3), or combinations thereof.
19. The system of claim 10, wherein the electrical segment inputs
comprise direct current signals.
20. The system of claim 10, wherein the electrical segment inputs
comprise alternating current signals.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of U.S.
Provisional Patent Application No. 62/041,544 filed Aug. 25, 2014,
by Yu Sheng Bai, and entitled, "Multi-Segment Mach-Zehnder
Modulator Driver System," which is incorporated herein by reference
as if reproduced in its entirety.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
REFERENCE TO A MICROFICHE APPENDIX
[0003] Not applicable.
BACKGROUND
[0004] Optical modulators are devices for modulating electrical
data signals onto an optical carrier to create an optical signal.
The modulation of the optical carrier may be performed by
manipulating a property of the optical carrier. Depending on which
property of the optical carrier is manipulated, the optical
modulators may be categorized into different types, for example,
intensity modulators for modifying optical signal amplitude, phase
modulators for modulating a phase of the optical carrier,
polarization modulators for modifying a polarization of the optical
carrier, and spatial light modulators for varying a spatial
property of the optical carrier.
SUMMARY
[0005] In one embodiment, the disclosure includes an optical
modulator comprising a waveguide for propagating an optical signal
comprising a proximate arm configured to communicate a proximate
portion of the optical signal, and a distal arm configured to
communicate a distal portion of the optical signal, a proximate
diode configured to modulate the proximate portion of the optical
signal, a distal diode configured to modulate the distal portion of
the optical signal, and an electrical input electrically coupled to
opposite signed interfaces of the proximate diode and the distal
diode such that an electrical driving signal propagated along the
electrical input causes an equal and opposite modulation of the
proximate portion of the optical signal in the proximate arm of the
waveguide and the distal portion of the optical signal in the
distal arm of the waveguide.
[0006] In another embodiment, the disclosure includes a
single-drive multi-segment optical modulator system comprising an
optical modulator comprising a plurality of electrical segment
inputs, a proximate waveguide arm configured to communicate a
proximate half of an optical signal, and a distal waveguide arm
configured to communicate a distal half of an optical signal, and a
plurality of modulator segments such that each modulator segment is
configured to modulate a corresponding electrical segment input
onto both the proximate waveguide arm and the distal waveguide arm,
and a drive circuit electrically coupled to the optical modulator
and comprising a plurality of drivers corresponding to the
plurality of modulator segments such that each driver outputs an
electrical segment signal to a single corresponding electrical
segment input to control modulation by a single corresponding
modulator segment.
[0007] These and other features will be more clearly understood
from the following detailed description taken in conjunction with
the accompanying drawings and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] For a more complete understanding of this disclosure,
reference is now made to the following brief description, taken in
connection with the accompanying drawings and detailed description,
wherein like reference numerals represent like parts.
[0009] FIG. 1 is a schematic diagram of an embodiment of a Z-cut
LiNbO.sub.3 MZM-driver system.
[0010] FIG. 2 is a schematic diagram of an embodiment of an X-cut
LiNbO.sub.3 MZM-driver system.
[0011] FIG. 3 is a schematic diagram of an embodiment of a
dual-drive multi-segment MZM-driver system.
[0012] FIG. 4 is a schematic diagram of an embodiment of a
single-drive multi-segment MZM-driver system.
[0013] FIG. 5 is a schematic diagram of another embodiment of a
single-drive multi-segment MZM-driver system.
[0014] FIG. 6 is a schematic diagram of an embodiment of a network
element (NE).
DETAILED DESCRIPTION
[0015] It should be understood at the outset that although an
illustrative implementation of one or more embodiments are provided
below, the disclosed systems and/or methods may be implemented
using any number of techniques, whether currently known or in
existence. The disclosure should in no way be limited to the
illustrative implementations, drawings, and techniques illustrated
below, including the exemplary designs and implementations
illustrated and described herein, but may be modified within the
scope of the appended claims along with their full scope of
equivalents.
[0016] An optical modulator is a building block in optical
communication systems. Optical modulators may be employed to enable
optical systems for various applications, such as optical sensing,
radio-frequency (RF) waveform generation for optical signal
transmission, and optical signal processing. Among various optical
modulators, Mach-Zehnder modulators (MZM) may be employed in
optical communications. There are at least four parameters to
characterize an optical modulator: V.sub..pi., insertion loss,
modulation speed, and modulation efficiency. V.sub..pi. is a change
in voltage required to achieve a .pi. phase shift in an optical
signal. A small V.sub..pi. indicates that a small voltage induces a
large phase shift, so an optical modulator with a small V.sub..pi.
consumes relatively low power. Insertion loss is defined as the
power loss due to the insertion of the optical modulator into a
system and is proportional to the length of the optical modulator.
Modulation speed corresponds to the maximum data rate of RF signals
that the optical modulator can modulate onto the optical signal.
Modulation efficiency indicates the rate of bits that can be
encoded into a waveform and is inversely proportional to the
product of V.sub..pi. and L, where L is the length of the optical
modulator required to achieve a .pi. phase shift. In other words, a
high modulation efficiency corresponds to a small product of
V.sub..pi. and L.
[0017] Disclosed herein are various embodiments for single-drive
multi-segment modulator-driver systems with high modulation
efficiency. The disclosed embodiments comprise a drive IC and a
multi-segment modulator. The optical modulator in any of the
embodiments herein comprises silicon, Indium Phosphide (InP),
Gallium Arsenide (GaAs), lithium niobate (LiNbO.sub.3), or
combinations thereof. The multi-segment modulator is suitable for
high speed operations (e.g., >25 Gigabits per second (Gbps)
modulation speed) and may be divided to a plurality of modulator
segments. Each modulator segment may encode a portion of an
electrical signal onto an optical carrier. Each modulator segment
comprises a modulation element coupled to a proximate arm of an
optical waveguide and a modulation element coupled to a distal arm
of the optical waveguide. The proximate and distal arms are coupled
together to allow modulated signal portions from both modulation
elements in each modulation segment to be aggregated into a single
optical signal. In an embodiment, the modulation elements are
diodes (e.g. a proximate diode and a distal diode). A single
electrical output from a single signal driver is coupled to each
modulation segment. For example, the electrical output is coupled
to a cathode of the proximate diode and to an anode of the distal
diode, or vice versa. Since the diodes are electrically oriented in
opposite directions (from the perspective of the driver), the
electrical signal from the driver is applied to each waveguide arm
in equal and opposite directions (e.g. different sign but same
absolute value), which allows a single driver to replace a dual
driver modulator system for each segment with no loss in modulation
amplitude. By removing the extra driver, modulation properties for
high speed applications can be achieved with reduced power, in a
reduced space, with fewer components/lower product cost, etc. In an
alternate embodiment, a single driver with two outputs may be
employed for each modulation segment to double the modulation power
applied to each waveguide arm without increasing the number of
drivers.
[0018] FIG. 1 is a schematic diagram of an embodiment of a Z-cut
LiNbO.sub.3 MZM-driver system 100, where Z-cut indicates the
polarization of crystals in the MZM is oriented in a Z-axis
direction perpendicular to the surface as shown in FIG. 1. The
Z-cut MZM-driver system 100 comprises a Z-cut MZM 101 and a pair of
complementary drivers comprising a proximate driver 110, and a
distal driver 135. Therefore, the Z-cut MZM 101 is sometimes
referred to as a dual-drive MZM. The Z-cut MZM-driver system 100
may be configured as shown or in any other suitable manner. The
Z-cut MZM 101 may be made of various materials. The materials may
include ferroelectric or electro-optical crystals such as lithium
niobate (LiNbO.sub.3). The Z-cut MZM 101 comprises an input optical
waveguide 105, a proximate arm waveguide 120, a distal arm
waveguide 130, a proximate electrode 140 coupled to the proximate
arm waveguide 120, a distal electrode 160 coupled to the distal arm
waveguide 130, grounds 150, and an output waveguide 170.
[0019] The input optical waveguide 105 is configured to receive
light and/or a modulated optical signal, communicate a proximate
half/portion of the optical signal to the proximate arm waveguide
120, and communicate a distal half/portion of the optical signal to
the distal arm waveguide 130, respectively. The proximate arm
waveguide 120 is electrically coupled to the proximate electrode
140, and the distal arm waveguide 130 is electrically coupled to
the distal electrode 160. The proximate arm waveguide 120 and the
distal arm waveguide 130 are configured to communicate the
proximate portion of the optical signal and the distal portion of
the optical signal, respectively, across the electrodes 140 and
160, respectively, for modulation and on to the output waveguide
170. The output waveguide 170 is configured to aggregate the
proximate portion of the optical signal and the distal portion of
the optical signal and communicate the combined optical signal, for
example for output to an external component such as another
waveguide, a waveguide-fiber coupler coupled to an optical fiber,
etc.
[0020] The proximate electrode 140 is coupled to the proximate
driver 110. The proximate driver 110 is configured to receive a
proximate RF signal 102, amplify the proximate RF signal 102 to
create an amplified proximate RF signal 115, and electrically
communicate the amplified proximate RF signal 115 to the proximate
electrode 140. The proximate electrode 140 and the ground 150 are
collectively configured to modulate the phase of the proximate
portion of the optical signals by depleting free electrons in the
proximate arm waveguide 120. Phase modulation of the proximate
portion of the optical signals is implemented by applying the
amplified proximate RF signal 115 on the proximate arm waveguide
120 to selectively deplete (e.g. depletion mode) or introduce free
electrons (e.g. accumulation mode) into the proximate arm waveguide
120, thereby inducing changes of the refractive index of the
proximate arm waveguide 120. The changes in the refractive index of
the proximate arm waveguide 120 alters the speed of the optical
signals propagating through the proximate arm waveguide 120,
resulting in the phase modulation of the optical signals. The
distal driver 135 receives and amplifies a distal RF signal 104 to
create an amplified distal RF signal 137 and communicates the
amplified distal RF signal 137 to the distal electrode 160 to
modulate optical signals in the distal arm waveguide 130 in a
substantially similar manner. Accordingly, the output of optical
signals in the proximate arm waveguide 120 and the distal arm
waveguide 130 can be combined into an optical output signal by
independently operating the proximate driver 110 and the distal
driver 135 using a push-pull operation.
[0021] The amplitude of the phase modulation of the proximate
portion of the optical signals and the distal portion of the
optical signals are positively proportional to the voltages of the
amplified proximate RF signal 115 and the amplified distal RF
signal 137, respectively, relative to grounds 150. The proximate RF
signal 102 and the distal RF signal 104 have a phase difference of
about 180 degrees. As a result, the phase modulations of the
proximate portion of the optical signals and the distal portion of
the optical signals have the same absolute values but different
signs. In one embodiment, the proximate RF signal 102 and the
distal RF signal 104 are generated by two different RF oscillators.
In another embodiment, the proximate RF signal 102 and the distal
RF signal 104 are generated by the same RF oscillator and one of
the RF signals (e.g. the distal 104) experiences a phase shift of
180 degrees with respect to the proximate RF signal due to an RF
shifter.
[0022] In operation, the optical signals are directed to the input
optical waveguide 105 and split into the proximate portion and the
distal portion. The proximate portion of the optical signals
travels in the proximate arm waveguide 120 and experiences a
proximate phase modulation. The distal portion of the optical
signals is communicated in the distal arm waveguide 130 and
experiences a distal phase modulation. The amplitudes of the
proximate phase modulation and the distal phase modulation have the
same absolute values but different signs. Then the proximate
portion of the optical signals is combined with the distal portion
of the optical signals at the output optical waveguide 170 for
communication to an external component.
[0023] FIG. 2 is a schematic diagram of an embodiment of an X-cut
LiNbO.sub.3 MZM-driver system 200, where X-cut indicates the X-axis
direction is perpendicular to the surface as shown in FIG. 2, while
the Z-axis (the polarization of the crystal) is perpendicular to
the optical waveguides. The X-cut MZM-driver system 200 comprises
an X-cut MZM 201 and a driver 210. The driver 210 is similar to the
proximate driver 110 and the distal driver 135. The X-cut MZM 201
is sometimes referred to as a single drive MZM. The X-cut
MZM-driver system 200 may be configured as shown or in any other
suitable manner. The X-cut MZM 201 may be substantially similar to
Z-cut MZM 101 with a different crystal polarization and comprises
an input optical waveguide 205, a proximate arm waveguide 220, a
distal arm waveguide 230, grounds 250, and an output waveguide 260,
which are similar to the input optical waveguide 105, the proximate
arm waveguide 120, the distal arm waveguide 130, grounds 150, and
the output waveguide 170, respectively.
[0024] The X-cut MZM 201 comprises an electrode 240, which is
substantially similar to electrodes 140 and 160, but is positioned
between the proximate arm waveguide 220 and the distal arm
waveguide 230. The electrode 240 is electrically coupled to driver
210. The driver 210 receives RF signal 204, amplifies the signal to
create an amplified RF signal 215, and applies the amplified RF
signal 215, via the electrode 240, between the proximate arm
waveguide 220 and the distal arm waveguide 230. The amplified RF
signal 215 depletes or induces free electrons in the proximate arm
waveguide 220 and the distal arm waveguide 230 between the
electrode 240 and the grounds 250. The polarizations of crystals in
the proximate arm waveguide 220 and the distal arm waveguide 230
are configured in opposite directions along the Z-axis resulting in
equal and opposite behavior (e.g. depletion or introduction of free
electrons) when the amplified RF signal 215 is applied to the
electrode. For example, the phase shifts of the optical carrier
portions that travel in the proximate arm waveguide 220 and the
distal arm waveguide 230 have the same absolute values but
different signs. As such, optical carriers traversing both the
proximate arm waveguide 220 and the distal arm waveguide 230 can be
controlled in a push-pull manner by a single driver 210.
Accordingly, the X-cut MZM 201 generates the same amount of phase
modulation as the Z-cut MZM 101 with fewer drivers given the same
voltage and electro-optical coefficients. The benefits of the X-cut
MZM-driver system 201 include simpler implementations, smaller
total sizes of a whole driver-modulator system, and lower power
consumptions.
[0025] In both the Z-cut MZM 101 and the X-cut MZM 201, the
capacitances in the proximate arm waveguides 120 and 220 and the
distal arm waveguides 130 and 230 are relatively large. As a
result, the applications of the Z-cut MZM 101 and the X-cut MZM 201
at high speeds (e.g., >25 Gbps modulation speed) are limited,
since the modulation speed is inversely proportional to the
capacitances. In addition, the propagation velocity of the RF
signals traveling in the MZMs are far slower than the propagation
velocity of the optical signals due to the large capacitances per
unit length, since the propagation velocity of the RF signals
traveling in the MZM is inversely proportional to the square root
of the capacitance per unit length.
[0026] FIG. 3 is a schematic diagram of an embodiment of a
dual-drive multi-segment MZM-driver system 300. The dual-drive
multi-segment MZM-driver system 300 comprises a drive integrated
circuit (IC) 310 and a multi-segment modulator 360. The dual-drive
multi-segment MZM-driver system 300 can be configured as shown or
in any other suitable manner. The dual-drive multi-segment
MZM-driver system 300 employs a plurality of modulator segments
370, each with an aggregate capacitance that is substantially
smaller than the capacitance of Z-cut MZM 101 and X-cut MZM 201.
The modulator segments 370 are synchronized by introducing timing
delay(s) to a proximate RF signal 320 and a distal RF signal 325 to
account for propagation delays of an optical signal traversing the
multi-segment modulator 360. As such, dual-drive multi-segment
MZM-driver system 300 may be modulated at higher speeds than Z-cut
MZM 101 and X-cut MZM 201.
[0027] The drive IC 310 comprises segment drivers 350 for each
modulator segment 370, wherein the segment drivers 350 are
electrically coupled via transmission lines 345. The segment
drivers 350 each comprise a proximate output 352 and a distal
output 354 (e.g. two drivers) that modulate a corresponding
modulator segment 370 in a push-pull manner similar to proximate
driver 110 and distal driver 135. The segment drivers 350 each
generate a proximate output 352 and a distal output 354 by
employing a proximate RF signal 320 and a distal RF signal 325
received via transmission lines 345 and input driver 340. The
proximate RF signal 320 and the distal RF signal 325, are similar
to the proximate RF signal 102 and the distal RF signal 104,
respectively. The drive IC 310 employs input driver 340 to amplify
the proximate RF signal 320 and the distal RF signal 325 as needed
for transmission via transmission lines 345. Input driver 340 may
operate in conjunction with grounded resistors 330 and 335 (e.g. 50
ohms (.OMEGA.) resistors) to perform impedance matching to prevent
electrical characteristics of devices supplying the proximate RF
signal 320 and the distal RF signal 325 from altering the
electrical characteristics of drive IC 310. The transmission lines
are coupled via resistor 342 to complete the circuit of the
transmission lines 345. The drive IC 310 is coupled to a power
source (e.g. a 5.2 volt (V) source) and a ground to receive
operational power. The drive IC 310 is controlled via direct
current (DC) controls 312 and 314 in the example shown. It should
be noted that while eleven segment drivers 350 are shown, any
number of segment drivers 350 can be employed to correspond with
the number of modulator segments 370.
[0028] The multi-segment modulator 360 comprises a proximate arm
waveguide 380 and a distal arm waveguide 390, which are similar to
proximate arm waveguides 120 and 220 and distal arm waveguides 130
and 230, respectively. The proximate arm waveguide 380 and the
distal arm waveguide 390 propagate an optical carrier via modulator
segments 370 and a bias segment 365. Each modulator segment 370
comprises a pair of capacitors 376 positioned on or adjacent to
each of the proximate arm waveguide 380 and the distal arm
waveguide 390. Each capacitor 376 on the proximate arm waveguide
380 (e.g. the proximate capacitor) is electrically coupled to the
proximate output 352 of the corresponding segment driver 350 and
each capacitor 376 on the distal arm waveguide 390 (e.g. the distal
capacitor) is electrically coupled to the distal output 354 of the
corresponding segment driver 350. Accordingly, each capacitor 376
can deplete or augment the electrons in the corresponding waveguide
arm 380/390 to modulate a portion/stage of the optical signal in a
push-pull fashion in a manner similar to Z-cut MZM 101 based on the
outputs of segment drivers 350. The modulator segments 370 further
comprise inductors 372 and resistors 374 for conditioning the
proximate output 352 and the distal output 354 sent to the
capacitors 376. Each capacitor 376 is also coupled to a voltage
source (or ground, depending on the embodiment) to manage
depletion/augmentation across the waveguide arms. The bias segment
365 provides any needed corrective conditioning of the optical
signal. The bias segment 365 comprises capacitors 368 for
modulating the optical signal based on Mach-Zehnder Interferometer
(MZI) bias controls 362 and 364, as well as resistors 366 for
conditioning the MZI bias signals as needed. The MZI bias controls
362 and 364 modulate the optical signal in a manner substantially
similar to modulator segments 370, but are employed for fine tuning
of the modulated signal before the signal is aggregated for
output.
[0029] In operation, the proximate RF signal 320 and the distal RF
signal 325 are timed and propagated to each segment driver 350 and
forwarded to each modulator segment 370 for modulation onto an
optical carrier. As the optical carrier propagates along the
waveguide arms 380 and 390, the optical carrier is modulated at
each modulator segment 370. The proximate RF signal 320 and the
distal RF signal 325 are timed so that the signals arrive at an
appropriate modulator segment 370 at an appropriate point in time
to match the velocity of the optical carrier, such that a complete
modulated optical signal is received at the bias segment 365 for
final aggregation and output. The multi-segment modulator 360
reduces the capacitance per segment compared to Z-cut MZM 101 and
X-cut MZM 201, but requires dual segments drivers 350 for each
modulator segment 370.
[0030] FIG. 4 is a schematic diagram of an embodiment of a
single-drive multi-segment MZM-driver system 400. The single-drive
multi-segment MZM-driver system 400 operates in a manner similar to
dual-drive multi-segment MZM-driver system 300, but employs a
segment driver 440 for each modulator segment 470. The single-drive
multi-segment MZM-driver system 400 may be employed for high speed
operations (e.g. larger than 25 Gigahertz (GHz)), but requires less
power and less complexity than system 300. The single-drive
multi-segment MZM-driver system 400 is configured as shown, or in
any other suitable manner, and comprises a drive IC 410 and a
multi-segment modulator 460.
[0031] The drive IC 410 comprises an input driver 430, segment
drivers 440, and a transmission line 450 for propagating an RF
input signal 420, which are similar to input driver 340, segment
drivers 350, and transmission lines 345, respectively. Drive IC 410
differs from drive IC 310 as drive IC 410 contains a single RF
input signal 420 and a single segment driver 440 for each modulator
segment 470 of the multi-segment modulator 460. Drive IC 410 may
also comprise resistors/inductors for impedance matching, DC
controls and/or a power supply as needed. While eleven segment
drivers 440 are shown, any number of segment drivers 440 can be
employed to correspond with the number of modulator segments 470.
The segment drivers 440 may be implemented as complementary
metal-oxide-semiconductor (CMOS) invertors, which consume
relatively low power. Each segment driver 440 receives a single
input and communicates a single output. A time delay between the
segment drivers 440 for velocity matching with the optical signal
is provided to transmission line 450 by the RF input signal 420.
The delay can also be generated actively by one or more CMOS
circuits. By selectively disabling the segment drivers 440 over
time (e.g. output set to low or high), a multi-level optical
signal, such as pulse amplitude modulation (PAM) can be generated,
even if the outputs of the drivers 440 have only two electrical
levels.
[0032] The multi-segment modulator 460 may be made of silicon,
Indium Phosphide (InP), and/or or Gallium Arsenide (GaAs). The
multi-segment modulator 460 comprises a proximate arm waveguide 480
and a distal arm waveguide 490, which are similar to proximate arm
waveguide 380 and distal arm waveguide 390, respectively, modulated
by a plurality of modulator segments 470 corresponding to the
segment drivers 440. Each modulator segment 470 comprises a
proximate diode 476 and a distal diode 475, positioned on/adjacent
to the proximate arm waveguide 480 and the distal arm waveguide
490, respectively. The diodes 475 and 476 may also be referred to
as positive-negative (p-n) diodes, and may act as voltage
controlled variable capacitors. The diodes 475 and 476 may be
oriented in with the same polarity as an X-cut MZM 201. The diodes
475 and 476 each comprise a negatively charged cathode and a
positively charged anode. Each segment driver 440 may be coupled to
the cathode of the proximate diode 476 and the anode of the distal
diode 475, as shown in FIG. 4. Alternately, each segment driver 440
may be coupled to the anode of the proximate diode 476 and the
cathode of the distal diode 475. In either case, the segment driver
440 is coupled to a negative portion of one diode and a positive
portion of the other diode such that each diode in a segment pair
has an opposite polarity with respect to the segment driver 440.
The interface of each diode that is not coupled to a segment driver
440 may be coupled to a ground to support alternating current (AC)
signals. DC isolation may be employed so that the diodes are biased
at desired DC voltages. For example, DC isolation can be
implemented by inserting large capacitors between each diode 475
and 476 and the respective ground. Because the polarity of the
diode on each arm is aligned oppositely with each other in
reference to the signal connection point, a driving signal results
in an opposite phase shift, but in equal value, on each arm of the
waveguide. As such, a single segment driver 440 generates the same
amount depletion/accumulation (and hence modulation) on each
waveguide arm as a pair of segment drivers 350. Accordingly, by
coupling the segment drivers 440 to a pair of oppositely charged
diodes 475 and 476, the number of transmission lines 450 and
segment drivers 440 can be reduced by half when compared with
dual-drive multi-segment MZM-driver system 300, while maintaining
the same modulation power, optical signal amplitude, modulation
speed, etc.
[0033] FIG. 5 is a schematic diagram of another embodiment of a
single-drive multi-segment MZM-driver system 500. The single-drive
multi-segment MZM-driver system 500 is substantially similar to
single-drive multi-segment MZM-driver system 400, but each segment
driver 540 of the drive IC 510 employs both a primary output and a
complementary output based on a single RF input signal 520 received
via an input buffer 530 and a transmission line 550. The primary
output is the same as the complementary output, but comprises an
opposite electrical charge/sign. For example, if the primary output
is about +0.5 volts, the complementary output is about -0.5 volts
at the same time. The drive IC 510, the RF input signal 520, the
input buffer 530, transmission line 550, and segment drivers 540,
may otherwise be substantially similar to drive IC 410, RF input
signal 420, input driver 430, transmission line 450, and segment
drivers 440, respectively. The single-drive multi-segment
MZM-driver system 500 may further comprise a multi-segment
modulator 560 comprising a proximate arm waveguide 580, distal arm
waveguide 590, and modulator segments 570 comprising distal diodes
575 and proximate diodes 576, which may be similar to multi-segment
modulator 460, proximate arm waveguide 480, distal arm waveguide
490, modulator segments 470, distal diodes 475, and proximate
diodes 476, respectively. The primary output of each segment driver
540 is coupled to the cathode of the proximate diode 576 and the
anode of the distal diode 575 while the complementary output is
coupled to the anode of the proximate diode 576 and the cathode of
the distal diode 575, or vice versa (e.g. the primary output is
coupled to different interfaces than the complementary output). By
replacing the ground connections from modulator segments 470 with a
complementary output, the effective driving voltage of each
modulator segment 570 is doubled without increasing the number of
segment drivers 540 or transmission lines 550. Similar to that in
FIG. 4, DC isolations may be employed so that the diodes are biased
at desired DC voltages. By doubling the voltage of the output to
each modulator segment 570 a larger differential phase shift and
thus higher modulation depth may be achieved resulting in greater
modulation efficiency. Further, the length of the MZM may be
shortened resulting in greater modulation efficiency.
[0034] FIG. 6 is a schematic diagram of an embodiment of a network
element (NE) 600. The NE 600 includes ingress ports 610 and
receiver units (Rx) 620 for receiving data, a processor, logic
unit, or central processing unit (CPU) 630 to process the data;
optical transmitter units (Tx) 640 and egress ports 650 for
modulating the data on optical signals and transmitting the optical
signals; and a memory 660 for storing the data. The Tx 640 may
comprise the single-drive multi-segment MZM-driver systems 400
and/or 500. The network element 600 may be configured as shown or
in any other suitable manner.
[0035] The processor 630 is configured to process the data and is
in communication with the ingress ports 610, receiver units 620,
transmitter units 640, egress ports 650, and memory 660. The memory
660 includes one or more disks, tape drives, and solid-state drives
and may be used as an over-flow data storage device, to store
programs when such programs are selected for execution, and to
store instructions and data that are read during program execution.
The memory 660 may be volatile and non-volatile and may be
read-only memory (ROM), random-access memory (RAM), ternary
content-addressable memory (TCAM), and static random-access memory
(SRAM).
[0036] In some embodiments, the NE 600 is programmed to generate
the proximate RF signal 102 and the distal RF signal 104. In some
embodiments, the NE 600 is programmed to generate the RF signal
204. In some embodiments, the NE 600 is programmed to generate the
proximate RF signal 320, the distal RF signal 325, the MZI bias
controls 362 and 364, and the DC controls 312 and 314. In some
embodiments, the NE 600 is programmed to generate the RF signal
420. In some embodiments, the NE 600 is programmed to generate the
RF signal 520.
[0037] It is understood that by programming and/or loading
executable instructions onto the NE 600, at least one of the
processor 630 and/or memory device 660 are changed, transforming
the NE 600 in part into a particular machine or apparatus, e.g. a
multi-core forwarding architecture, having the novel functionality
taught by the present disclosure. It is fundamental to the
electrical engineering and software engineering arts that
functionality that can be implemented by loading executable
software into a computer can be converted to a hardware
implementation by well-known design rules. Decisions between
implementing a concept in software versus hardware typically hinge
on considerations of stability of the design and numbers of units
to be produced rather than any issues involved in translating from
the software domain to the hardware domain. Generally, a design
that is still subject to frequent change may be preferred to be
implemented in software, because re-spinning a hardware
implementation is more expensive than re-spinning a software
design. Generally, a design that is stable that will be produced in
large volume may be preferred to be implemented in hardware, for
example in an ASIC, because for large production runs the hardware
implementation may be less expensive than the software
implementation. Often a design may be developed and tested in a
software form and later transformed, by well-known design rules, to
an equivalent hardware implementation in an ASIC that hardwires the
instructions of the software. In the same manner as a machine
controlled by a new ASIC is a particular machine or apparatus,
likewise a computer that has been programmed and/or loaded with
executable instructions may be viewed as a particular machine or
apparatus.
[0038] While several embodiments have been provided in the present
disclosure, it should be understood that the disclosed systems and
methods might be embodied in many other specific forms without
departing from the spirit or scope of the present disclosure. The
present examples are to be considered as illustrative and not
restrictive, and the intention is not to be limited to the details
given herein. For example, the various elements or components may
be combined or integrated in another system or certain features may
be omitted, or not implemented.
[0039] In addition, techniques, systems, subsystems, and methods
described and illustrated in the various embodiments as discrete or
separate may be combined or integrated with other systems, modules,
techniques, or methods without departing from the scope of the
present disclosure. Other items shown or discussed as coupled or
directly coupled or communicating with each other may be indirectly
coupled or communicating through some interface, device, or
intermediate component whether electrically, mechanically, or
otherwise. Other examples of changes, substitutions, and
alterations are ascertainable by one skilled in the art and could
be made without departing from the spirit and scope disclosed
herein.
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